BLACK holes should never be stripped naked. If the interior was exposed it could unleash cosmic chaos, but the reassuring news is that nature has confounded the latest idea for uncloaking one.
For decades, a debate has raged as to whether the interior of a black hole could ever be exposed. This could expose a singularity – a point of infinite density made from the scrunched remains of whatever collapsed to form the black hole – where the known laws of physics break down. For all we know, the singularity could be spitting out an apple pie, or an orchestra playing Beethoven’s ninth symphony, but we don’t see such effects because the black hole’s tremendous gravity keeps them locked inside. If a singularity were to be unleashed, it could potentially throw the orderly universe we know into disarray, and show that the universe’s properties are not as predictable as we thought.
According to a proposed law of physics called the weak censorship conjecture, it should never be possible to expose a naked singularity. Yet no one has ever proved the conjecture, and there have been many attempts to invent clever ways to expose one. One proposal for how it could be done involves giving a black hole a strong electric charge, which would push things away by electrostatic repulsion. However, it has been shown that the black hole would spontaneously purge itself of charge just before it strips.
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“It may prove impossible to expose a naked singularity but that hasn’t stopped people inventing clever ways to try”
Last November, George Matsas and André da Silva of São Paulo State University in Brazil calculated that you could beat this purging effect by inducing a nearly fully charged black hole to spin faster. Aim an additional particle so that it was absorbed off-centre, they argued, and the black hole’s spin would increase enough that it hurls its outer layers outwards (Physical Review Letters, ).
Now Shahar Hod of the Ruppin Academic Center in Emeq Hefer, Israel, reckons he has found a flaw in this proposal. He has shown that the final particle would be repelled rather than absorbed, and so fail to give the black hole enough spin. That’s because the particle would induce a minute gravitational tug on the black hole before the two collide, Hod says, a fact which Matsas and da Silva failed to consider. This interaction would give the black hole a spin too feeble to throw out material, yet strong enough to make the particle bounce off instead of being absorbed (Physical Review Letters, ).
The black hole naturally defeats the attempt, Hod says, just as it has done for previous ideas. “It seems every time we think we have finally found a sophisticated way of violating the cosmic censorship conjecture, nature still has the final word.”
Matsas argues that the final particle could in principle still be absorbed if it was a neutrino, which has a specific quantum “spin” that would prevent its deflection. “The whole issue is not settled yet,” he says.
